Temperature drawing preparation method and device for magnesium alloy thin-wall micro pipe

Abstract

The invention discloses a hot drawing preparation method and device for a magnesium alloy thin-wall micro pipe. The device comprises a quartz tube, a quartz plate placed in the quartz tube, a heating belt wound outside the quartz tube, a slidable rack for placing the quartz tube, a die holder which is concentric with the quartz tube on the same horizontal line, a drawing die placed in the die holder, a heating coil wound outside the die holder, and a control power supply for supplying power to the heating belt and the heating coil, the device is used for carrying out cold drawing, annealing, hot drawing and annealing on the magnesium alloy pipe blank. According to the device, a dual heating mode is realized, so that the temperature fields of the magnesium alloy pipe and the drawing die are consistent, and meanwhile, a cold drawing and hot drawing combined mode is adopted, so that the precision and the plastic processing capacity of the magnesium alloy pipe are effectively improved. According to the temperature drawing preparation method carried out through the device, the thin-wall micro magnesium alloy pipe with high size precision and excellent performance can be more efficiently produced.

Description

Technical Field

[0001] The invention belongs to the field of magnesium alloy processing, and in particular relates to a method and a device for preparing magnesium alloy thin-wall micro-tubes by warm drawing. Background Art

[0002] Thin-walled micro-magnesium alloy tubes have broad application prospects in the biomedical field, so the efficient preparation of high-quality thin-walled micro-magnesium alloy tubes has become a research hotspot in the field of magnesium alloy processing. At present, multi-pass cold drawing of tube blanks is the mainstream process for preparing biological magnesium alloy micro-tubes. However, due to the fact that magnesium has a close-packed hexagonal structure, only basal slip and two twin modes are activated at room temperature and lower temperatures, which cannot meet the requirements of the five independent slip systems required for plastic deformation. The deformation capacity at room temperature is poor, resulting in a lengthy cold drawing process, and multiple heat treatments between passes, which is not conducive to the control of the micro-tube structure and properties of the tube. In addition, biological magnesium alloy tubes are prone to cracks due to large axial tensile stress during cold drawing; while increasing the temperature, the conical and cylindrical slip systems can be activated, the deformation capacity of magnesium alloys can be improved, the reduction in a single pass can be increased, and the initiation of microcracks can be reduced. However, due to the skin effect, it is difficult to achieve a uniform temperature field in this method, resulting in temperature imbalance between the tube surface and the long mandrel, and it is difficult to heat the drawing die. Therefore, it is urgent to explore the uniform heating of micro-tubes and drawing dies during the drawing process to form tubes. Summary of the invention

[0003] In order to solve the above problems, the present invention first provides a device for preparing magnesium alloy thin-walled micro-tubes by warm drawing. The device realizes a double heating method to make the temperature field of the magnesium alloy tube and the drawing die consistent. At the same time, it adopts a combination of cold drawing and hot drawing to effectively improve the precision and plastic processing ability of the magnesium alloy tube.

[0004] The present invention also provides a method for preparing magnesium alloy thin-walled micro-tubes by warm drawing. The method adopts the above-mentioned device to more efficiently produce thin-walled micro-magnesium alloy tubes with high dimensional accuracy and excellent performance by warm drawing.

[0005] The present invention is achieved through the following technical solutions: A device for preparing magnesium alloy thin-walled micro-tubes by warm drawing, the device comprising a quartz tube (7), a quartz plate (11) placed inside the quartz tube (7), a heating belt (9) wound around the outside of the quartz tube (7), a slidable frame (13) on which the quartz tube (7) is placed, a die base (4) which is coaxial with the quartz tube (7), a drawing die (6) placed inside the die base (4), a heating coil (3) wound around the outside of the die base (4), and a control power supply (12) for supplying power to the heating belt (9) and the heating coil (3); The right end of the quartz tube (7) can slide through a slidable frame (13) to fit with the left end of the mold base (4); The inner diameter of the left side of the die base (4) matches the outer diameter of the drawing die (6); The quartz plate (11) has a width matching the inner diameter of the quartz tube (7) and is inserted into the quartz tube (7) to ensure that it is on the same horizontal line as the mold base (4); a thermocouple (10) for measuring the outer wall temperature of the tube blank is provided on the quartz tube (7); and a lubrication hole (8) for dripping lubricant is provided on the quartz tube; The die base (4) is provided with a temperature measuring device (2) for measuring the temperature of the drawing die; A drawing trolley (5) is arranged on the same horizontal line as the outlet of the die base (4).

[0006] Furthermore, the thickness of the mold base heating part is 10-15 mm, and the wall thickness of the quartz tube is 3-5 mm.

[0007] Furthermore, a plurality of drawing dies of different sizes can be placed in the die base.

[0008] Furthermore, the drawing die is made of die steel, and the die base is made of 40Cr steel.

[0009] The present invention also provides a method for preparing magnesium alloy thin-wall micro-tubes by warm drawing using the above-mentioned device, the method comprising the following steps: S1: taking a magnesium alloy tube blank and a steel mandrel, cleaning the surfaces to remove surface impurities and oil stains, and then inserting the steel mandrel into the magnesium alloy tube blank to obtain a combination (1); the length of the mandrel is greater than the length of the tube blank; S2: placing the assembly (1) described in step S1 in the above-mentioned device for preparing magnesium alloy thin-walled micro-tubes by warm drawing for drawing, specifically as follows: Slide the quartz tube (7) to the left side of the die base, place a suitable drawing die (6) in the die base and add lubricant through the lubrication hole (8) to lubricate the outer surface of the assembly (1), then insert the head of the assembly (1) through the drawing die (6), pass through the die base (4) and clamp it on the drawing trolley (5) of the drawing machine, place the other end of the assembly (1) on the quartz plate (11) inside the quartz tube (7), then slide the quartz tube (7) through the slidable frame (13) so that its right end fits with the left end of the die base (4); S3: Turn on the drawing trolley of the drawing machine to drive the assembly to run at a constant speed for cold drawing, while dripping lubricant through the lubrication hole (8); S4: repeating steps S2 and S3 until the magnesium alloy tube billet and the steel mandrel are tightly fitted; S5: placing the assembly obtained after cold drawing in step S4 into a tubular furnace for annealing; S6: Repeat step S2 for the assembly annealed in step S5, and turn on the control power of the quartz tube and the heating coil, set the heating temperature to 100-300°C, and after the temperature reaches the set temperature, turn on the drawing trolley of the drawing machine to drive the assembly to run at a constant speed for warm drawing, while dripping lubricant through the lubrication hole (8); S7: placing the assembly after warm drawing in step S6 in a tube furnace for annealing; S8: Repeat steps S6 and S7 on the assembly annealed in step S7 until the target outer diameter and wall thickness are reached, and then remove the mandrel to obtain a magnesium alloy microtube.

[0010] Furthermore, the magnesium alloy tube blank described in step S1 may be ZE21B magnesium alloy, ZE21C magnesium alloy, WE43C magnesium alloy, EK20M magnesium alloy, etc.; the steel mandrel may be made of spring steel, die steel or stainless steel; Furthermore, in step S1, the inner and outer surface roughness Ra of the magnesium alloy tube blank is less than 3.2 μm, the outer surface roughness Ra of the steel mandrel is less than 3.2 μm, the outer diameter of the tube blank is 2.8-3.5 mm, and the wall thickness of the tube blank is 0.2-0.3 mm; the diameter of the steel mandrel is 1.95-2.7 mm, and the length of the steel mandrel is not less than 1200 mm.

[0011] Furthermore, the head of the assembly (1) is ground before drawing to ensure that it can pass through the drawing die (6) and be clamped by the drawing trolley (5); Furthermore, in the device of step S2, the assembly, die base, drawing die, drawing trolley and quartz tube are strictly concentric to improve the uniformity of the wall thickness of the tube after drawing.

[0012] Furthermore, the drawing speed of the cold drawing in step S3 is 0.5-2 mm / s, and the deformation of a single pass of cold drawing is not greater than 20%; and the lubricant is graphene grease or high temperature resistant lubricating oil.

[0013] Furthermore, the deformation amount of a single pass of the warm drawing in step S6 is 20-40%, and the drawing speed of each drawing pass is 0.5-2 mm / s.

[0014] Furthermore, argon gas is introduced into the tube furnace in step S5 and step S7, and annealing is performed at an annealing temperature of 260-340° C. for 30-60 min.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. The method of the present invention has high production efficiency, saves time and labor, and reduces production difficulty.

[0016] 2. In the present invention, dynamic recovery occurs during the warm drawing process, eliminating the work hardening effect, while activating the cylindrical and conical slip systems and improving the deformation capacity of the magnesium alloy microtube.

[0017] 3. The warm drawing adopted in the present invention can effectively increase the deformation amount of a single pass in the drawing process, effectively reduce the number of drawing passes and the number of heat treatments, improve the drawing efficiency, and shorten the pipe processing cycle.

[0018] 4. The present invention combines cold drawing with warm drawing, which can effectively improve the uniformity of tube wall thickness and surface quality, and prepare bio-magnesium alloy thin-wall microtubes with high dimensional accuracy and excellent performance.

[0019] 5. The device of the present invention achieves consistency in the temperature of the tube and the mold, and the quality of the prepared magnesium alloy tube is significantly improved and uniform. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0021] Figure 1 It is a schematic diagram of the overall structure of the warm drawing forming device of the present invention; Figure 2 It is a schematic diagram of the internal structure of the warm drawing forming device of the present invention; Figure 3 Macroscopic images of the tubes obtained in the cold drawing example and Examples 2 to 4 of the present invention; Figure 4 This is a diagram showing the measurement results of the wall thickness uniformity of the tubes obtained in the cold drawing embodiment and embodiments 2 to 4 of the present invention; Figure 5 This is a diagram showing the straightness measurement results of the pipes obtained in the cold drawing embodiment and embodiments 2 to 4 of the present invention; Figure 6 The diagram is a measurement result diagram of the cross section and the maximum deformation of a single pass of the tube obtained in the cold drawing embodiment and embodiments 2 to 4 of the present invention; Figure 7 It is a graph showing the measurement results of microcracks on the surface of the tubes obtained in the cold drawing example and Examples 2 to 4 of the present invention.

[0022] Description of reference numerals: 1—assembly; 2—temperature measuring device; 3—heating coil; 4—die base; 5—drawing trolley; 6—drawing die; 7—quartz tube; 8—lubricating hole; 9—heating belt; 10—temperature measuring device; 11—quartz plate; 12—control power supply; 13—sliding frame DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further described below in conjunction with specific embodiments, but does not constitute a limitation of the present invention. Specific conditions not described in the following examples are all carried out according to conventional conditions or conditions recommended by manufacturers. Example 1

[0024] This embodiment provides a device for preparing magnesium alloy thin-walled micro-tubes by warm drawing, the device comprising a quartz tube (7), a quartz plate (11) placed inside the quartz tube (7), a heating belt (9) wound around the outside of the quartz tube (7), a slidable frame (13) for placing the quartz tube (7), a die base (4) on the same horizontal line and concentric with the quartz tube (7), a drawing die (6) placed inside the die base (4), a heating coil (3) wound around the outside of the die base (4), and a control power supply (12) for supplying power to the heating belt (9) and the heating coil (3); The right end of the quartz tube (7) can slide through a slidable frame (13) to fit with the left end of the mold base (4); The inner diameter of the left side of the die base (4) matches the outer diameter of the drawing die (6); The quartz plate (11) has a width matching the inner diameter of the quartz tube (7) and is inserted into the quartz tube (7) to ensure that it is on the same horizontal line as the mold base (4); a thermocouple (10) for measuring the outer wall temperature of the tube blank is provided on the quartz tube (7); and a lubrication hole (8) for dripping lubricant is provided on the quartz tube; The die base (4) is provided with a temperature measuring device (2) for measuring the temperature of the drawing die; A drawing trolley (5) is arranged on the same horizontal line as the outlet of the die base (4).

[0025] The thickness of the heating portion of the mold base (4) is any value between 10 and 15 mm, and the wall thickness of the quartz tube is any value between 3 and 5 mm.

[0026] Drawing dies of different sizes can be placed in the die base.

[0027] The drawing die used in the device is made of die steel, and the die base is made of 40Cr steel. Example 2

[0028] The device described in Example 1 was used to prepare magnesium alloy thin-walled micro-tubes by warm drawing, as follows: 1) A tube blank made of ZE21B magnesium alloy, with a diameter of 3.30 mm, a wall thickness of 0.2 mm, and a length of 800 mm, needs to be drawn with a core into a tube with a diameter of 2.78 mm, a wall thickness of 0.14 mm, and a length of 1000 mm. The core shaft has a diameter of 2.5 mm and a length of 1500 mm. The core shaft is inserted into the tube blank to obtain a combination (1); 2) Grinding the assembly head of the assembly (1) obtained in step 1) to ensure that it can pass through the drawing die and be clamped by the drawing trolley; 3) Select 3.10 and 2.90 mm drawing dies in turn and place them in the die base, insert the head of the assembly through the drawing die, pass through the die base and clamp it on the fixture of the drawing machine, place the other side of the assembly on the quartz plate inside the quartz tube, then slide the quartz tube to the left side of the right die base to overlap, start the drawing carriage to cold draw in sequence at a rate of 0.5 mm / s, and drip high temperature resistant lubricating oil (about one drop per second) through the lubrication hole (8) on the quartz tube during the cold drawing process; repeat the operation until the magnesium alloy tube billet fits tightly with the steel mandrel; 4) placing the assembly drawn by the 3.10 and 2.90 mm drawing dies in step 3) in an annealing furnace protected by argon gas for annealing at 280° C. for 30 min; 5) Select 2.83 mm and 2.78 mm drawing dies in turn and place them in the die base. Insert the head of the assembly obtained after annealing in step 4) through the drawing die, pass through the die base and clamp it on the drawing trolley (5) of the drawing machine. Place the other side of the assembly on the quartz plate inside the quartz tube. Then slide the quartz tube to the left side of the right die base to overlap. Start the control power supply and set the temperature to 100°C. After the temperature of the heating belt and the heating coil are both stable at 100°C, start the drawing trolley and perform warm drawing at a rate of 0.5 mm / s. During the warm drawing process, drip graphene grease (about one drop per second) through the lubrication hole (8) on the quartz tube. 6) placing the assembly drawn in step 5) in an annealing furnace protected by argon gas for annealing at 320° C. for 30 min; 7) The tail mandrel of the assembly obtained in step 6) is passed through the drawing die with an inner diameter of 2.60 mm in the opposite direction and placed in the die base. The drawing trolley of the drawing machine is turned on to drive the assembly to run at a constant speed to remove the mandrel and obtain a finished magnesium alloy microtube.

[0029] Finally, a magnesium alloy tube with an outer diameter of 2.78 mm, a wall thickness of 0.14 mm, and a length of 1070 mm was obtained through the above processing technology. Example 3

[0030] The device described in Example 1 was used to prepare magnesium alloy thin-walled micro-tubes by warm drawing, as follows: 1) The material is ZE21C, the tube blank with a diameter of 3.50 mm, a wall thickness of 0.3 mm, and a length of 500 mm needs to be drawn with a core into a tube with a diameter of 2.78 mm, a wall thickness of 0.14 mm, and a length of 1000 mm. The mandrel has a diameter of 2.5 mm and a length of 1500 mm. The mandrel is inserted into the tube blank to obtain a combination (1); 2) Grind the head of the assembly obtained in step 1) to ensure that it can pass through the drawing die and be clamped by the drawing trolley; 3) Select 3.30 mm and 3.10 mm drawing dies in turn and place them in the die base, insert the head of the assembly through the drawing die, pass through the die base and clamp it on the drawing trolley (5) of the drawing machine, place the other side of the assembly on the quartz plate inside the quartz tube, then slide the quartz tube to the left side of the right die base to overlap, start the drawing trolley to cold draw in turn at a rate of 0.5 mm / s, and drip graphene grease (about one drop per second) through the lubrication hole (8) on the quartz tube during the cold drawing process; repeat the operation until the magnesium alloy tube billet fits tightly with the steel mandrel; 4) placing the assembly drawn by the 3.30 and 3.10 mm drawing dies in step 3) in an annealing furnace protected by argon gas for annealing at 280° C. for 30 min; 5) Select 3.0, 2.9, 2.8, and 2.78 mm drawing dies in turn and place them in the die base. Insert the head of the assembly obtained after annealing in step 4) through the drawing die, pass through the die base and clamp it on the fixture of the drawing machine. Place the other side of the assembly on the quartz plate inside the quartz tube. Then slide the quartz tube to the left side of the right die base to overlap. Start the control power supply and set the temperature to 200°C. After the temperature of the heating belt and the heating coil are both stable at 200°C, start the drawing carriage and perform warm drawing in sequence at a rate of 0.5 mm / s. During the warm drawing process, drip graphene grease (about one drop per second) through the lubrication hole (8) on the quartz tube. 6) placing the assembly drawn in step 5) in an annealing furnace protected by argon gas for annealing at 320° C. for 30 min; 7) The tail mandrel of the assembly obtained in step 6) is passed through the drawing die with an inner diameter of 2.60 mm in the opposite direction and placed in the die base. The drawing trolley of the drawing machine is turned on to drive the assembly to run at a constant speed to remove the mandrel and obtain a finished magnesium alloy microtube.

[0031] Finally, a pure magnesium tube with an outer diameter of 2.78 mm, a wall thickness of 0.14 mm, and a length of 1030 mm was obtained through the above processing technology. Example 4

[0032] The device described in Example 1 was used to prepare magnesium alloy thin-walled micro-tubes by warm drawing, as follows: 1) The material is EK20C, the tube blank is 3.40 mm in diameter, 0.25 mm in wall thickness and 600 mm in length, and needs to be drawn with a core into a tube with a diameter of 2.78 mm, a wall thickness of 0.14 mm and a length of 1000 mm. The mandrel has a diameter of 2.5 mm and a length of 1500 mm. The mandrel is inserted into the tube blank to obtain a combination (1); 2) Grind the head of the assembly obtained in step 1) to ensure that it can pass through the drawing die and be clamped by the drawing trolley; 3) Select 3.2 and 3.0 mm drawing dies in turn and place them in the die base, insert the head of the assembly through the drawing die, pass through the die base and clamp it on the drawing trolley (5) of the drawing machine, place the other side of the assembly on the quartz plate inside the quartz tube, then slide the quartz tube to the left side of the right die base to overlap, start the drawing trolley to cold draw in turn at a rate of 0.5 mm / s, and drip graphene grease (about one drop per second) through the lubrication hole (8) on the quartz tube during the cold drawing process; repeat the operation until the magnesium alloy tube billet fits tightly with the steel mandrel; 4) placing the assembly drawn by the 3.2 and 3.0 mm drawing dies in step 3) in an annealing furnace protected by argon gas for annealing at 280° C. for 30 min; 5) Select 2.87 mm and 2.78 mm drawing dies in turn and place them in the die base. Insert the head of the assembly obtained after annealing in step 4) through the drawing die, pass through the die base and clamp it on the fixture of the drawing machine. Place the other side of the assembly on the quartz plate inside the quartz tube. Then slide the quartz tube to the left side of the right die base and overlap it. Start the control power supply and set the temperature to 300°C. After the temperature of the heating belt and the heating coil are both stable at 300°C, start the drawing carriage and perform warm drawing at a rate of 0.5 mm / s. During the warm drawing process, drip graphene grease (about one drop per second) through the lubrication hole (8) on the quartz tube. 6) placing the assembly drawn in step 5) in an annealing furnace protected by argon gas for annealing at 320° C. for 30 min; 7) The tail mandrel of the assembly obtained in step 6) is passed through the drawing die with an inner diameter of 2.60 mm in the opposite direction and placed in the die base. The drawing trolley of the drawing machine is turned on to drive the assembly to run at a constant speed to remove the mandrel and obtain a finished magnesium alloy microtube.

[0033] Finally, a magnesium alloy tube with an outer diameter of 2.78 mm, a wall thickness of 0.14 mm, and a length of 1070 mm was obtained through the above processing technology.

[0034] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention. Example 5

[0035] The magnesium alloy thin-walled micro-tube is prepared by cold drawing process using conventional equipment, as follows: 1) A magnesium alloy tube blank with an outer diameter of 3.30 to 3.50 mm and a wall thickness of 0.20 to 0.30 mm obtained by hot extrusion is matched with a steel mandrel with an outer diameter of 2.50 mm and a length of 1500 mm, and the mandrel is inserted into the magnesium alloy hot extruded tube blank to obtain an assembly (1); 2) First pass of cold drawing: Place a 3.10 mm or 3.20 mm or 3.30 mm drawing die into the die base, pass the assembly (1) through the drawing die, pass through the die base and clamp it on the drawing trolley (5) of the drawing machine, place the other side of the assembly on the quartz plate inside the quartz tube, then slide the quartz tube to the left side of the right die base to overlap, start the drawing trolley to perform cold drawing at a rate of 0.5 mm / s, and drip graphene grease through the lubrication hole during the cold drawing process (the deformation of a single cold drawing pass is not more than 10%); 3) annealing the assembly after the first cold drawing in step 2) in an annealing furnace protected by argon gas at 280° C. for 30 min; 4) Second cold drawing pass: Place a 2.90 mm, 3.00 mm or 3.10 mm drawing die into the die base, and repeat the operation of step 2) to obtain a cold drawn assembly; 5) Repeat the annealing operation of step 3) on the assembly obtained in step 4) until the magnesium alloy tube billet and the steel mandrel are tightly fitted to obtain a cold-drawn assembly.

[0036] The magnesium alloy thin-wall microtubes in this test example were all prepared by the above method.

[0037] The macroscopic images of the bio-magnesium alloy microtubes obtained by cold drawing in Example 5 and Examples 2 to 4 are as follows Figure 3 shown. Figure 3 The end face image (left image) of the bio-magnesium alloy microtube produced in each embodiment and the length direction image of the bio-magnesium alloy microtube produced in each embodiment are shown in the figure. It can be seen from the figure that the bio-magnesium alloy microtubes produced in Examples 2 to 4 can meet the requirements of inner and outer diameters and lengths.

[0038] Example 5 Cold drawing and the biological magnesium alloy microtube wall thickness deviation test obtained in Examples 2 to 4 are as follows Figure 4 shown. Figure 4 The results are obtained by measuring the uniformity of the wall thickness of the bio-magnesium alloy microtubes produced by cold drawing and in each embodiment. Figure 4 It can be seen that the wall thickness uniformity of the cold-drawn tube is greater than 4%, and the wall thickness deviation of the magnesium alloy micro-tubes produced in each embodiment is less than 4%, which can meet the wall thickness uniformity requirement.

[0039] Example 5 Cold drawing and the straightness test of the microtubes obtained in Examples 2 to 4 are as follows Figure 5 shown. Figure 5 The straightness test results of magnesium alloy microtubes produced by cold drawing and in various embodiments are shown in Table 1. Figure 5 It can be seen that the straightness deviation of the magnesium alloy microtubes produced by cold drawing and each embodiment is less than 2 mm / m, and the straightness increases with the increase of the drawing temperature.

[0040] The single-pass deformation ability test of the bio-magnesium alloy microtubes obtained by cold drawing in Example 5 and Examples 2 to 4 is as follows Figure 6 shown. Figure 6 The figures are respectively the bar graph of the maximum shrinkage reduction of cold drawing at temperature and the single-pass drawing of each embodiment, and the cross-section of the microtube before and after the single-pass maximum shrinkage reduction drawing. Figure 6 (b) It can be seen that compared with the magnesium alloy micro-tubes of each embodiment, the maximum reduction in a single pass of cold drawing continues to increase, indicating that with the increase of drawing temperature, dynamic recovery occurs, eliminating the work hardening effect and improving the single-pass deformation capacity of the magnesium alloy micro-tubes.

[0041] Example 5 Cold drawing and analysis of microcracks on the surface of bio-magnesium alloy microtubes obtained in Examples 2 to 4 are as follows Figure 7 shown. Figure 7 The types of surface microcracks generated during the drawing process of the bio-magnesium alloy are: transverse cracks perpendicular to the drawing direction (a) and oblique cracks at a certain angle to the drawing direction (b); and the statistical diagram of the number of microcracks in 100mm micro-tubes and tube blanks after cold drawing and the same drawing temperature of each embodiment with a single-pass deformation of 17.24%. Figure 7 (c) It can be seen that compared with cold drawing, warm drawing can reduce the generation of microcracks, and the number of microcracks continues to decrease with the increase of drawing temperature. The number of microcracks at 300°C is equivalent to the number on the surface of the tube blank, which shows that warm drawing can greatly reduce the stress concentration on the surface of the biological magnesium alloy microtube during the drawing process, so that the initiation of microcracks during the drawing process is greatly reduced. In summary, the magnesium alloy tube prepared by the warm drawing method of the present invention has an outer diameter of 2.25 ~ 3.00mm, a wall thickness of 0.12 mm ~ 0.15mm, a wall thickness deviation of <4%, a straightness of <2mm / m, and a length of more than 1000mm, which meets the process parameter requirements of medical cardiovascular stents, and can significantly improve the deformation ability of microtubes, the deformation amount of a single pass in the drawing process, reduce the number of drawing passes, reduce the number of heat treatments, improve the drawing efficiency, and reduce the drawing cost. It has good application prospects in the field of biological magnesium alloy microtube processing.

Claims

1. A device for preparing magnesium alloy thin-walled micro-tubes by warm drawing, characterized in that: The device comprises a quartz tube (7), a quartz plate (11) placed inside the quartz tube (7), a heating belt (9) wound around the outside of the quartz tube (7), a slidable frame (13) on which the quartz tube (7) is placed, a die base (4) which is on the same horizontal line and concentric with the quartz tube (7), a drawing die (6) placed inside the die base (4), a heating coil (3) wound around the outside of the die base (4), and a control power supply (12) for supplying power to the heating belt (9) and the heating coil (3); The right end of the quartz tube (7) can slide through a slidable frame (13) to fit with the left end of the mold base (4); The inner diameter of the left side of the die base (4) matches the outer diameter of the drawing die (6); The quartz plate (11) has a width matching the inner diameter of the quartz tube (7) and is inserted into the quartz tube (7) to ensure that it is on the same horizontal line as the mold base (4); a thermocouple (10) for measuring the outer wall temperature of the tube blank is provided on the quartz tube (7); and a lubrication hole (8) for dripping lubricant is provided on the quartz tube; The die base (4) is provided with a temperature measuring device (2) for measuring the temperature of the drawing die; A drawing trolley (5) is arranged on the same horizontal line as the outlet of the die base (4).

2. The device according to claim 1, characterized in that The thickness of the mold base heating part is 10-15 mm, and the wall thickness of the quartz tube is 3-5 mm.

3. The device according to claim 1, characterized in that Drawing dies of different sizes can be placed in the die base.

4. The device according to any one of claims 1 to 3, characterized in that: The drawing die is made of die steel, and the die base is made of 40Cr steel.

5. A method for preparing magnesium alloy thin-walled micro-tubes by warm drawing using the device according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: S1: taking a magnesium alloy tube blank and a steel mandrel and cleaning the surfaces thereof, and then inserting the steel mandrel into the magnesium alloy tube blank to obtain a combination (1); wherein the length of the mandrel is greater than the length of the tube blank; S2: placing the assembly (1) described in step S1 in a device for preparing magnesium alloy thin-walled micro-tubes by warm drawing for drawing, specifically as follows: Slide the quartz tube (7) to the left, place it in a suitable drawing die (6), and add lubricant through the lubrication hole (8) to lubricate the surface of the assembly (1), then insert the head of the assembly (1) through the drawing die (6), pass through the die base (4) and clamp it on the drawing trolley (5) of the drawing machine, and place the other end of the assembly (1) on the quartz plate (11) inside the quartz tube (7), and then slide the quartz tube (7) through the slidable frame (13) so that its right end fits with the left end of the die base (4); S3: Turn on the drawing trolley of the drawing machine to drive the assembly to run at a constant speed for cold drawing, while dripping lubricant through the lubrication hole (8); S4: repeating steps S2 and S3 until the magnesium alloy tube billet and the steel mandrel are tightly fitted; S5: placing the cold-drawn assembly in step S4 into a tubular furnace for annealing; S6: Repeat step S2 for the assembly annealed in step S5, then turn on the control power of the quartz tube and the heating coil, set the heating temperature to 100-300°C, and after the temperature reaches the set temperature, turn on the drawing trolley of the drawing machine to drive the assembly to run at a constant speed for hot drawing, while dripping lubricant through the lubrication hole (8); S7: placing the assembly after warm drawing in step S6 in a tube furnace for annealing; S8: Repeat steps S6 and S7 on the assembly annealed in step S7 until the target outer diameter and wall thickness are reached, and then remove the mandrel to obtain a magnesium alloy microtube.

6. The method according to claim 5, characterized in that In step S1, the inner and outer surface roughness of the magnesium alloy tube blank Ra is less than 3.2 μm, the outer surface roughness of the mandrel Ra is less than 3.2 μm, the outer diameter of the tube blank is 2.8-3.5 mm, and the wall thickness of the tube blank is 0.2-0.3 mm; the diameter of the mandrel is 1.95-2.7 mm, and the length of the mandrel is not less than 1200 mm.

7. The method according to claim 5, characterized in that The cold drawing speed in step S3 is 0.5-2 mm / s, and the single-pass deformation of cold drawing is not more than 20%; the lubricant is graphene grease or high-temperature resistant lubricating oil.

8. The method according to claim 5, characterized in that The deformation amount of a single pass of the warm drawing in step S6 is 20-40%, and the drawing speed of each drawing pass is 0.5-2 mm / s.

9. The method according to claim 5, characterized in that In step S5 and step S7, argon gas is introduced into the tubular furnace, and annealing is performed at an annealing temperature of 260-340° C. for 30-60 min.

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